1. Field of the Invention
The present invention relates to a transfer charger transferring a toner image held by an image holder to an intermediate transfer belt and an image-forming apparatus.
2. Description of the Related Art
The image-forming apparatus is known in which a toner image held by the image holder is transferred to the intermediate transfer belt to obtain an image. The image-forming apparatus adopts a method of transferring the toner image held by the image holder to the intermediate transfer belt nipped by the image holder and a transfer roller.
There is formed a portion where the intermediate transfer belt and the transfer roller confront each other with a small gap interposed therebetween in the neighborhood of a portion where the intermediate transfer belt and the transfer roller contact each other. A transfer electric field having an unclear boundary is formed in the portion where the small gap is formed. Such an unclear transfer electric field can be a factor deteriorating transfer performance. For example, such an unclear transfer electric field causes the toner image to be scattered upstream from a transfer region. A transfer blade which contacts an inner surface of the intermediate transfer belt opposite to the transfer surface thereof to which the toner image is transferred is known (see patent document 1). The portion of the transfer blade where it confronts the intermediate transfer belt with the small gap interposed therebetween is very small. A small transfer electric field having the unclear boundary is formed in the gap formed between the transfer blade and the intermediate transfer belt unlike the above-described construction. Thus the above-described transfer performance little deteriorates. But there is a fear that the transfer efficiency deteriorates because an image-forming apparatus using the transfer blade has a narrow transfer region.
Instead of the transfer blade, the edge of which contacts the intermediate transfer belt, there is proposed the transfer member capable of making a surface contact with the intermediate transfer belt (see patent documents 2 and 3). The transfer member is rectangular solid-shaped. The material of the film which can be used for the surface of the transfer member which contacts the intermediate transfer belt is disclosed in the patent document 2.
But the transfer member disclosed in the patent document 2 makes the surface contact with the inner surface of the intermediate transfer belt in a large area. Thereby the transfer member has a large frictional resistance and contacts the intermediate transfer belt uncontinuously with the movement of the intermediate transfer belt. As a result, the generation of a transfer electric field may become unstable. Unless the frictional resistance of the transfer member is stable, an image deviation occurs. In some cases, there is a possibility that the transfer member is removed from a holder or broken.    Patent document 1: Japanese Patent Application Laid-Open No. 2007-41242    Patent document 2: Japanese Patent Application Laid-Open No. 09-120218    Patent document 3: Japanese Patent Application Laid-Open No. 2007-156455